There is a case in which, for the purpose of coping with such as increase of a data transmission volume and improvement of redundancy to enhance availability, a communication system having a communication device connected to a network via a plurality of ports is used. In a communication system which performs communication using a plurality of communication routes on a network, it is desirable that, when load increase or a failure occurs in a communication route, a time needed for switching of ports of a communication device be suppressed as much as possible to improve availability or to reduce delay. It is also desirable that a communication route can be selected appropriately according to a load of a network and available communication routes.
There is a case where a communication device connected to a network by a plurality of ports has a load balancer function for conducting data transmission in a distributed manner among each port. However, even when conducting communication while making a plurality of communication routes share a load, a loss of a packet and delay of transmission can be caused if a communication route is not selected appropriately. It is necessary to suppress a loss of a packet and delay of transmission as much as possible because they deteriorate quality of communication. Therefore, development of technologies which suppress, in a communication system which performs communication via a plurality of communication routes, a loss of a packet and delay of transmission while sharing a load has been made. As a technology which suppresses a loss of a packet and delay of transmission while sharing a load in a communication system communicating via such a plurality of communication routes, the technology of patent document 1 (Japanese Patent Application Laid-Open No. 2009-55419), for example, has been disclosed.
Patent document 1 relates to a communication system in which a transmitting device and a receiving device communicate via a plurality of networks. A transmitting device and a receiving device of a communication system of patent document 1 are connected with each other via a plurality of networks. In a communication system of patent document 1, a plurality of ports of a transmitting device and a plurality of ports of a receiving device correspond to each other in one-on-one, respectively, and are connected to each network. A transmitting device of patent document 1 shares a load and performs communication by assigning a packet to be transmitted to each port in turn.
A receiving device of patent document 1 detects a loss of packets received via each port by monitoring packets held in a buffer provided for each port based on a sequence number. When a packet loss is detected, a receiving device of patent document 1 requests a communication device to retransmit a packet. In patent document 1, it is supposed that, by having such structure, influence of a packet loss in a communication system which shares a load and communicates by a plurality of routes can be suppressed.
However, the technology of patent document 1 is not sufficient in the following point. In a communication system of patent document 1, ports of a transmitting device and a receiving device are combined fixedly in one-on-one, respectively. In addition, each pair of ports corresponds to different networks, respectively. Therefore, the technology of patent document 1 cannot handle a case in which, in a communication system equipped with a communication device connected to a single network via a plurality of ports, a route is reorganized at the time of a failure and the like. Furthermore, because, in patent document 1, packets to be transmitted are allocated to each port in turn, packets are allocated even to a network of a heavy load. Therefore, in a communication system of patent document 1, there is a fear that delay occurs in transmission of a packet. Therefore, the patent document 1 is not enough as a technology for suppressing a loss of a packet and delay of transmission while sharing a load in a communication system which communicates via a plurality of routes.